It is oftentimes desirable, or necessary, to load material into a holding receptacle and then later remove the stored material from the receptacle.
While this is not a difficult problem with some materials, such as liquids, or even with some solid state materials, problems have arisen where the material to be handled and stored is a material that is subject to damage by impact during handling. Such a material, for example, could be any granular or pelleted material including grain, seeds and nuts and/or could be chemicals or the like that might be damaged by impact during handling.
In handling of grains, a grain ladder has heretofore been utilized to introduce grain into a storage receptacle, with withdrawal of the grain being commonly from the bottom of the receptacle.
The grain ladder is a device designed to slow the descent of grain (or seeds or other granular of free-flowing materials) into the storage receptacle (or processing, conditioning or holding chamber or vessel). Such a ladder typically consists of one or more rectangular (or square) tubes, or passages, that are vertically positioned and attached to the walls of the receptacle for support with the passages generally being positioned out of the primary grain flow path when the receptacle is unloaded by withdrawal of stored material through an outlet in, or near, the base of the receptacle.
The grain or material ladder derives its name from the fact that the passage into which the material is introduced for flow downward into the storage, or holding, receptacle is equipped with a series of internal baffles to retard the flow and maintain descent velocity below that critical for damage as the grain, seed or material impacts on the mass accumulated in the receptacle. The baffles usually project alternately from two opposite inside surfaces of the ladder passage, and are spaced at alternate points along the passage length. The resultant flow path forms a zig-zag pattern, and the continual change in flow direction as the material descends slows the flow velocity. Such a ladder is normally equipped with outlet ports, which are cut out of the tube wall at points between the locations or elevations of the baffles.
In operation, material descends slowly down the zig-zag ladder inside the ladder passage until it reaches the level of that accumulated in the storage receptacle. At this point, the ladder tube outlet is blocked by accumulated material, and the tube starts to fill. With outlet ports spaced at frequent intervals, the passage fills only to the level of the next higher outlet, resulting in a very short drop onto the accumulated material mass in the storage receptacle.
Grain and material ladders, as now known and normally used, are positioned along the wall of the storage receptacle for support, and to insure that they will be out of the primary grain flow path when the storage is unloaded. The purpose is to minimize the frictional drag on the outside surface of the ladder, which may bring about structural distortion or complete failure and collapse of the ladder assembly as the material flows around and along the tube, or passage, during unloading. Such collapse may also damage the storage structure or associated handling equipment.
Positioning of the grain or material ladder on one or more inside walls of the storage, or holding, receptacle requires that the wall of the receptacle be capable of sustaining of the unbalanced sidewall loading due to the angle of repose of the material. For most free-flowing grains and seeds, this angle of repose is typically 25.degree. to 30.degree. above horizontal. This will result in roughly a 15 foot fill height on the inside of the storage receptacle at the grain ladder for a 30 foot wide structure. This unbalanced loading may cause the wall of the storage receptacle to distort and possibly cause total structural failure by collapse or tipping.
Since many grains, seeds and nuts and a number of free-flowing materials are stored in thin wall structures and vessels that require uniform sidewall loading essentially at all times for structural stability, such side mounted grain or material ladders or flow retarders now known cannot be used.